NSScrollView containing NSStackView. Why the NSStackView items from bottom to Top?

Question

The NSScrollView containing a NSStackView. The NSStackView's items will add in runtime.The new NSStackView's items are from bottom to top, but I want they are from top to bottom.

The main.storyboard

The ViewController

import Cocoa

class ViewController: NSViewController {

    var todoList:[Todo] = []

    @IBOutlet weak var todosStackView: NSStackView!
    @IBOutlet weak var todosScrollView: NSScrollView!

    @IBAction func onEnter(sender: NSTextField) {
        let todo = Todo()
        todo.content = sender.stringValue
        self.todoList.append(todo)

        let todoItemView = TodoItem()
        todoItemView.setButtonType(.SwitchButton)
        todoItemView.todo=todo
        todosStackView.addView(todoItemView, inGravity: .Top)
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }

    override var representedObject: AnyObject? {
        didSet {
        // Update the view, if already loaded.
        }
    }
}

The checkbox button class

import Cocoa

class TodoItem: NSButton {
    var todo:Todo!{
        didSet {
            self.title = self.todo.content
            self.state = self.todo.done ? NSOnState : NSOffState
        }
    }

    func completeTodo(){
        if(self.state == NSOnState){
            self.todo.done = true
        }else{
            self.todo.done = false
        }
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
    }

    override init(frame frameRect: NSRect) {
        super.init(frame: frameRect)
        self.setButtonType(.SwitchButton)
        self.target = self
        self.action = #selector(self.completeTodo)
    }
}

Answer 1

By default, NSClipViews (and the base NSView) are not flipped and so coordinates (and scroll view positioning) are relative to the bottom left.

You can subclass NSClipView and override isFlipped to return true. Then in IB, set the clip view of the scroll view to that custom class.